NTIA Technical Report TR-08-455 

Measurements to Characterize Land 

Mobile Channel Occupancy for Federal 

Bands 162–174 MHz and 406–420 MHz in 

the Denver, CO Area

John E. Carroll 

J. Randy Hoffman 

Robert J. Matheson 

NTIA Technical Report TR-08-455 

Measurements to Characterize Land 

Mobile Channel Occupancy for Federal 

Bands 162–174 MHz and 406–420 MHz in 

the Denver, CO Area

John E. Carroll 

J. Randy Hoffman 

Robert J. Matheson 

U.S. DEPARTMENT OF COMMERCE 

Carlos M. Gutierrez, Secretary 

Meredith Attwell Baker, Acting Assistant Secretary 

for Communications and Information 

September 2008 

DISCLAIMER 

Certain commercial equipment and materials are identified in this report to specify adequately 

the technical aspects of the reported results. In no case does such identification imply 

recommendations or endorsement by the National Telecommunications and Information 

Administration, nor does it imply that the material or equipment identified is the best available 

for this purpose. 

iii 

CONTENTS 

FIGURES ....................................................................................................................................... vi

TABLES ...................................................................................................................................... viii

ACRONYMS ................................................................................................................................. ix

DEFINITIONS .................................................................................................................................x

EXECUTIVE SUMMARY ......................................................................................................... xiii

1 INTRODUCTION ........................................................................................................................1

1.1 Objective ..........................................................................................................................2

1.2 Approach ..........................................................................................................................2

2 FIELD MEASUREMENTS DESCRIPTION...............................................................................4

2.1 Site Selection ....................................................................................................................4

3 ANALYSIS and RESULTS ..........................................................................................................7

3.1 Time Scenarios .................................................................................................................7

3.2 High Occupancy Channels ...............................................................................................7

3.3 Measurement Results .......................................................................................................8

3.3.1 Results for 162–174 MHz Band ......................................................................11

3.3.2 Results for 406–420 MHz Band ......................................................................22

4 SUMMARY ................................................................................................................................34

4.1 Overall Results ...............................................................................................................35

4.1.1 Results for 162–174 MHz band ......................................................................36

4.1.2 Results for 406–420 MHz band ......................................................................37

4.2 Diurnal Patterns for Both Bands ....................................................................................37

4.3 Evaluation of Measurement Techniques and Technologies ...........................................37

5 ACKNOWLEDGEMENTS ........................................................................................................38

6 REFERENCES ...........................................................................................................................38

APPENDIX A: SUPPLEMENTAL MEASUREMENT RESULTS .............................................39

A.1 Usage for Each One-hour Block During the Course of the Measurements ..................39

A.2 Percent Band Usage for the 162–174 MHz Band .........................................................41

A.3 Percent Band Usage for the 406–420 MHz Band .........................................................43

APPENDIX B: WASHINGTON DC AND DENVER, CO MEASUREMENT RESULTS 

COMPARISON TABLES .......................................................................................................45

v
FIGURES 

Page 

Figure 1. RSMS mobile lab at measurement location. ................................................................... 4

Figure 2. Aerial view of the Denver metropolitan area and the location of the measurement 

system. ............................................................................................................................................ 5

Figure 3. Coverage plot for the 162–174 MHz band using the minimum receiver threshold. ....... 6

Figure 4. Coverage plot for the 406–420 MHz band using the minimum receiver threshold. ....... 6

Figure 5. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 162–174 MHz band (minimum threshold). ............................................... 11

Figure 6. Busiest Hour of the Week for Each Channel in the 162–174 MHz band. ..................... 12

Figure 7. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during 

different 24-hour time scenarios in the 162–174 MHz band (minimum threshold, all channels 

spaced 12.5 kHz apart). ................................................................................................................. 13

Figure 8. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during the 

course of 24 hours, independent of the date, for different channelization scenarios in the 

162–174 MHz band (minimum threshold). .................................................................................. 14

Figure 9. Band Occupancy by Time-of-Day (percent of time and total Erlangs) using different 

thresholds, independent of the date, for all 943 channels in the 162–174 MHz band. ................. 15

Figure 10. Percent of Hourly Channel Percent Occupancy values exceeding a given percent 

usage over the course of the measurements for the 162–174 MHz band (minimum threshold). . 16

Figure 11. Percent of channels exceeding a given percent usage for Channel Percent 

Occupancy over the course of the measurements for the 162–174 MHz band (minimum 

threshold). ..................................................................................................................................... 17

Figure 12. Percent of channels exceeding a given percent usage for the Busiest Usage by 

Time-of-Day for Each Channel during weekdays only in the 162–174 MHz band 

(minimum threshold). ................................................................................................................... 18

Figure 13. APDs of Channel Power Values for channels in the 162–174 MHz band — entire 

week, independent of date or time for different channelizations (minimum threshold). .............. 19

Figure 14. APDs of Channel Power Values for all channels spaced 12.5 kHz apart in the 

162–174 MHz band for the busiest hour during the entire week independently for each 

frequency (minimum threshold). .................................................................................................. 20

vi
Figure 15. Cumulative distribution of the percent of channels that exceed a given percent of 

hours at greater than or equal to a given Hourly Channel Percent Occupancy (designated by 

legend) for all channels in the 162–174 MHz band (minimum threshold, entire week). ............. 21

Figure 16. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 406–420 MHz band (excluding HOCs; minimum threshold). .................. 22

Figure 17. Busiest Hour of the Week for Each Channel in the 406–420 MHz band. ................... 23

Figure 18. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 406–420 MHz band (including HOCs; minimum threshold). ................... 24

Figure 19. Band Occupancy by Time-of-Day during different 24-hour time scenarios in the 

406–420 MHz band (excluding HOCs; minimum threshold). ...................................................... 25

Figure 20. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during the 

course of 24 hours, independent of the date, for different channelization scenarios in the 

406–420 MHz band (excluding HOCs; minimum threshold). ...................................................... 26

Figure 21. Band Occupancy by Time-of-Day (percent of time and total Erlangs) using 

different thresholds, independent of the date, for all 1,100 channels in the 406–420 MHz 

band (excluding HOCs). ............................................................................................................... 27

Figure 22. Percent of Hourly Channel Percent Occupancy values exceeding a given percent 

usage over the course of the measurements for the 406–420 MHz band (minimum threshold). . 28

Figure 23. Percent of channels exceeding a given percent usage for Channel Percent Occupancy

over the course of the measurements for the 406–420 MHz band (minimum threshold). ........... 29

Figure 24. Percent of channels exceeding a given percent usage for the Busiest Usage by 

Time-of-Day for Each Channel during weekdays only in the 406–420 MHz band 

(minimum threshold). ................................................................................................................... 30

Figure 25. APDs of Channel Power Values for channels in the 406–420 MHz band — entire 

week, independent of date or time for different channelizations (excluding HOCs; minimum 

threshold). ..................................................................................................................................... 31

Figure 26. APDs of Channel Power Values for all channels spaced 12.5 kHz apart in the 

406–420 MHz band for the busiest hour during the entire week, independently for each 

frequency for different HOC scenarios (minimum threshold). ..................................................... 32

Figure 27. Cumulative distribution of the percent of channels that exceed a given percent of 

hours at greater than or equal to a given Hourly Channel Percent Occupancy (designated by 

legend) for all channels in the 406–420 MHz band (excluding HOCs; minimum threshold). ..... 33

Figure A-1. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for all 943 channels in the 162–174 MHz band. ................................................... 39

vii
viii

Figure A-2. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for all 1,100 channels in the 406–420 MHz band (excluding HOCs). .................. 40

TABLES 

Page 

Table 1. Total Number of Statistically Analyzed Channels Spaced 12.5 kHz Apart ..................... 7

Table 2. Figure Numbers for Graphs in the 162–174 MHz Band .................................................. 8

Table 3. Figure Numbers for Graphs in the 406–420 MHz Band .................................................. 9

Table 4. Minimum Threshold Values ........................................................................................... 10

Table A-1. Percent Band Usage and Average of Busiest Usage by Hour During the Entire 

Week for All 943 Channels in the 162–174 MHz Band ................................................................ 41

Table A-2. Percent Band Usage and Average of Busiest Usage by Hour During Weekdays 

Only for All 943 Channels in the 162–174 MHz Band ................................................................ 42

Table A-3. Percent Band Usage and Average of Busiest Usage by Hour During Weekend 

Days Only for All 943 Channels in the 162–174 MHz Band ....................................................... 42

Table A-4. Percent Band Usage and Average of Busiest Usage by Hour During the Entire 

Week for All 1,100 Channels in the 406–420 MHz Band (Excluding HOCs) ............................. 43

Table A-5. Percent Band Usage and Average of Busiest Usage by Hour During Weekdays 

for All 1,100 Channels in the 406–420 MHz Band (Excluding HOCs) ....................................... 44

Table A-6. Percent Band Usage and Average of Busiest Usage by Hour During Weekend 

Days for All 1,100 Channels in the 406–420 MHz Band (Excluding HOCs). ............................. 44

Table B-1. Usage Summary for Washington, DC and Denver Metropolitan Area 

Measurements in the 162–174 MHz LMR Band .......................................................................... 46

Table B-2. Usage Summary for Washington, DC and Denver Metropolitan Area 

Measurements in the 406–420 MHz LMR Band .......................................................................... 47
ACRONYMS 

APD amplitude probability distribution

dB decibel 

dBi decibels relative to isotropic 

dBm decibels relative to 1 milliwatt 

dBμV/m decibels relative to 1 microvolt per meter 

GMF Government Master File

HOC high occupancy channel

ITS Institute for Telecommunication Sciences 

kHz kilohertz 

km kilometer 

LMR Land Mobile Radio 

m meter 

MHz megahertz 

NTIA National Telecommunications and Information Administration 

OSM Office of Spectrum Management 

PSWAC Public Safety Wireless Advisory Committee

RF radio frequency

RSMS Radio Spectrum Measurement Science

RSMS-4 Radio Spectrum Measurement Science fourth generation measurement system 

W watt

ix
DEFINITIONS 

Amplitude Probability Distribution (APD): A cumulative probability distribution plot 

representing the probability of exceeding a given level of power, where the y-axis displays 

power and the x-axis displays the probability expressed on a Rayleigh scale. The tutorial in 

Appendix A of [1] provides a detailed description of APDs. 

Area Assignments: Frequency assignments in the Government Master File that do not have 

specific coordinates and authorize base station and/or mobile stations to operate anywhere within 

a defined geographic area (e.g., United States and Possessions). 

Average of Busiest Usage by Hour: Determined by computing the average of the Busiest Usage 

by Time-of-Day for Each Channel values across all channels in the band, resulting in a single 

value for the entire band. The Average of Busiest Usage by Hour values are displayed in 

Tables A-1, A-2, A-4, and A-5. 

Band Occupancy by Time-of-Day: Determined by taking the Hourly Band Usage values for 

each hour of the day, and computing the average for the corresponding hours of the measurement 

period. Band Occupancy by Time-of-Day values are displayed in Figures 7 through 9 and 19 

through 21. 

Busiest Usage by Time-of-Day for Each Channel: Determined for each channel by identifying 

the Usage by Time-of-Day value that is the largest out of the 24 values. There is only one Busiest 

Usage by Time-of-Day value for each channel. The Busiest Usage by Time-of-Day for Each 

Channel values are summarized in Figures 12 and 24. 

Busiest Hour of the Week for Each Channel: Determined for each channel by identifying the 

time and date at which the highest Hourly Channel Percent Occupancy value occurs. During the 

week, channels will typically have a different date and time when the usage is busiest. Busiest 

Hour of the Week for Each Channel values are displayed in Figures 6 and 17. 

Channel Percent Occupancy: Computed for each channel by determining the percent of 

Channel Power Values that exceed a detection threshold for each 1-second acquisition every day 

of the measurement period. For example, if 2,280 out of the 76,000 total Channel Power Values

for a specific channel are above the detection threshold, then the channel occupancy is 3 percent 

at that detection level for the specified channel. Channel Percent Occupancy values are 

summarized in Figures 11 and 23. 

Channel Power Readings: The amount of received power on an individual channel measured 

using an Agilent E4440A Spectrum Analyzer in a resolution bandwidth of 5.5 kHz. Five of these 

basic measurements are used to compute a Channel Power Value, which is the building block for 

all further analysis and computations. 

Channel Power Value: Determined by computing the median of 5 consecutive individual 

Channel Power Readings measured within a 1-second measurement period. The median value of 

the 5 independent measurements made for each channel is selected as the single value of 

measured power for that channel during that 1-second measurement period. All further 

x
processing of measured data is based on this median-of-5 measurement technique. For example, 

if the 5 individual Channel Power Readings are -77, -70, -75, -69, and -73 dBm, the median 

value is -73 dBm. This value is computed for each channel at 1-second intervals, in the 4-minute 

measurement period for each 5-MHz frequency block. Channel Power Values are summarized in 

Figures 13, 14, 25, and 26. 

Channel Power Values in an Hour: A set of individual Channel Power Values measured over a 

1-hour period. This is represented by a set of data that typically contains either 240 

(162–174 MHz band) or 480 (406–420 MHz band) median-of-5 Channel Power Values for that 

hour of that day for a specific channel. 

Erlangs: A traffic equivalent to full time occupancy of a channel for an hour – for instance, one 

channel used continuously for 60 minutes, or two channels with a combined occupancy of 

60 minutes. In this report, the number of Erlangs is determined by multiplying the percent usage 

by the total number of channels in the band. 

High Occupancy Channel: A channel that exceeds the detection threshold for a large percent of 

the time (defined in this paper as >80 percent of time). 

Hourly Band Usage: Determined by averaging all of the Hourly Channel Percent Occupancy

values in a given hour of a given day for all of the channels in the band. The Hourly Band Usage

is displayed in Figures 5, 16, 18, A-1, and A-2. 

Hourly Channel Percent Occupancy: Computed for each channel by determining the number 

of Channel Power Values in an Hour for a given channel that exceed a detection threshold. For 

example, if 14 out of 480 total Channel Power Values in an Hour are above the detection 

threshold, then the channel occupancy is 3 percent at that detection level, for the specified hour 

and channel. Hourly Channel Percent Occupancy values are summarized in Figures 10, 15, 22, 

and 27. 

Hydrology Channel: A channel used for the automatic transmission of hydrologic or 

meteorological data, or both. Hydrology channels are present in the 162–174 MHz and the 406–

420 MHz LMR bands but are not considered LMR users.

Maximum Band Occupancy: The maximum of all Band Occupancy by Time-of-Day values. 

This is shown in Figures 8 and 20. 

Occupancy: Channels are considered occupied (i.e., in use) whenever the channel contains radio 

frequency power above a certain received detection threshold level. By some definitions a 

channel may be considered “in use” even if no traffic is being carried during the time of 

measurement. For instance, a channel being used by a Secret Service agent protecting the 

President may not carry traffic (not occupied) unless there is an emergency. However, the 

channel is “in use” in the sense that personnel are monitoring the channel and ready to take 

action should a situation require it. In this report, “usage” is used interchangeably with the term 

“occupancy,” which means “carrying traffic” — not simply being monitored. 

xi
Percent Band Usage: Determined by computing the mean of all Hourly Channel Percent 

Occupancy values for all channels during the measurement period. The measurement periods 

examined include all days, weekdays only, and weekend days. Percent Band Usage values are 

shown in Tables A-1 through A-6. 

Specific Location Assignments: Frequency assignments in the Government Master File that 

have specific coordinates (latitude and longitude) for the location of the base station and a radius 

of operation for the associated mobile and portable stations. 

Trunking: The method used in some modern communications systems in which frequency 

channels are assigned dynamically as required, usually when there are more users than available 

frequency channels. This allows time sharing of the same frequencies by multiple users, thus 

improving channel usage efficiency. Typically, a control channel is used to make initial contact, 

after which a frequency channel is assigned to the user’s radio device during the course of the 

connection. This technique is utilized in most modern cellular phone services, since there are far 

more users than available frequencies. 

Usage by Time-of-Day for Each Channel: Determined for each channel by computing the 

average of the Hourly Channel Percent Occupancy values for each specific hour of the day for 

the corresponding measurement period (e.g., all days, weekdays, and weekend days). For 

example, channel 1 will have 24 different Usage by Time-of-Day for Each Channel values, each 

for a different hour of the day. These 24 values represent the mean usage for that specific time of 

day over the course of the several days of the measurements. 

 

Usage: Refer to the definition for “Occupancy.” 

xii
EXECUTIVE SUMMARY 

In May 2003, President Bush established the Spectrum Policy Initiative to promote the 

development and implementation of a United States spectrum policy for the 21st century. In 

response to the Spectrum Policy Initiative, the Secretary of Commerce established a Federal 

Government Spectrum Task Force and initiated a series of public meetings to address policies 

affecting spectrum use by the Federal, state, and local governments, and the private sector. The 

recommendations resulting from these activities were included in two reports released by the 

Secretary of Commerce in June 2004. Based on the recommendations contained in these reports, 

the President directed the Federal Agencies on November 30, 2004 to plan the implementation of 

the 24 recommendations contained in the reports. One of the recommendations directed the 

National Telecommunications and Information Administration (NTIA) to develop analytic 

approaches, software tools, and engineering techniques for evaluating and improving the 

efficiency and effectiveness of Federal spectrum use. 

To satisfy one of the goals of that recommendation, NTIA’s Institute for Telecommunication 

Sciences (ITS) undertook a series of channel occupancy measurements in Arvada in the Denver, 

Colorado metropolitan area from October 26 to November 3, 2005 in the Land Mobile Radio 

(LMR) bands 162–174 and 406–420 megahertz (MHz). The purpose of these measurements was 

twofold: first, to evaluate and refine LMR channel occupancy measurement techniques, 

previously developed for the Washington, DC LMR measurements performed in 2004; secondly, 

to gather actual data on the usage of these bands in the Denver metropolitan area. The data 

gathered for this area and these bands will be used for further analyses of other aspects of the 

Presidential Spectrum Policy Initiative. 

Measurements of LMR channels were conducted at a site on the grounds of the Exempla 

Colorado Lutheran Home facility, at a location in Arvada overlooking the Denver metropolitan 

area, using the fourth generation Radio Spectrum Measurement Science (RSMS) system. The 

measurements were conducted 24 hours per day over the course of 8 consecutive days. The 

measured data was then processed at the ITS Laboratory in Boulder, Colorado. 

The measurement system was designed to have a spatial coverage area of approximately 

100-kilometer (km) radius for base stations, 50-km radius for mobile units, and 25-km radius for 

handheld units. The results are reported in terms of channel usage for designated LMR channels, 

irrespective of whether the individual channels have been assigned or not. The purpose is to 

determine, given a specific threshold sensitivity, whether LMR channels at a location 

overlooking the Denver metropolitan area are being used at that location and to what extent. 

There are four types of data summarized in this report: 1) mean channel usage, 2) mean busiesthour statistics, 3) power-level statistics, and 4) statistics on percent of channels (and hourly 

channel usage) exceeding a given percent usage. 

The measured data contains information on channel usage for two types of frequency 

assignments: Specific Location Assignments and Area Assignments. Specific Location 

Assignments have specific coordinates (latitude and longitude) for the location of the base 

station and a radius of operation for associated mobile and portable stations. Area Assignments 

do not have specific coordinates and authorize base and mobile stations to operate anywhere 

xiii
within a specific geographic area (e.g., United States and Possessions). These two types of 

frequency assignments were not distinguished during analyses; therefore the usage statistics are 

based on both types of assignments. 

For the 162–174 MHz band, the mean percent time that all of the channels in the band are being 

used for each hour (referred to in this report as Band Occupancy by Time-of-Day) varied between 

0.6 and 1.5 percent, with the busiest hours being between 6 a.m. and 6 p.m. For the 

406–420 MHz band, the value was 0.6 to 1.0 percent with the busiest hours being between 6 a.m. 

and 3 p.m. 

The Band Occupancy by Time-of-Day for conventional LMR systems can be compared to 

allowable call-blockage (typically defined as Grade of Service) as recommended in the Final 

Report of the Public Safety Wireless Advisory Committee (PSWAC)[3]. In that report, the 

PSWAC recommends that call-blockage not exceed “one call for service per one hundred 

attempts during the average busy hour.” That translates to no more than 1 percent usage for 

multi-user conventional systems where channels are assigned statically. Since the existing 

systems measured in the 162–174 MHz band are conventional systems, the measured channel 

usage during the busiest hour of 1.3 percent is consistent with the recommendations made by the 

PSWAC. 

 

In the 162–174 MHz band, the diurnal behavior was similar, irrespective of whether they were 

measured for all days, weekdays, or weekends. The highest overall usage occurred on weekdays 

(Figure 7), with the normal daylight hours showing the most activity. Curiously, there was a 

duration of time in the mid-morning hours where the weekend use dominated the weekday use. 

In the 406–420 MHz band, a distinct difference in diurnal pattern can be noted between the 

weekday and weekend cases (Figure 19), with the usage being higher during normal daylight 

hours on the weekdays and the usage being higher outside of normal daylight hours on 

weekends. Usage on the weekends is decreased by a factor of as much as 2 during normal 

daylight hours when compared to weekdays. There was a small duration of time in the early 

morning hours where usage was higher for the weekend case when compared to the weekday 

case. 

It should be noted that most of the channels in these bands are statically assigned to networks or 

individual users, in contrast to dynamically assigned as is the case with trunked systems, where 

there is time sharing of each frequency channel by multiple users. Some of these assigned 

channels are reserved for high priority usage in which communication must be available at all 

times for a limited number of users, thus resulting in low percent usage. In addition, none of 

these measurements were made during a major emergency that might have greatly increased the 

use of radio channels. 

The data can be used for specifying the overall performance objectives of a hypothetical 

communications system using a different technology (e.g., trunking). By designing the 

hypothetical system to provide the same overall communications capability as the existing LMR 

systems, the existing and hypothetical systems could then be compared to examine relative total 

spectrum usage (number of channels required for each system). For example, in NTIA Report 

xiv
xv

08-451 [4], measurements of LMR usage for the 162–174 MHz band in the Washington, DC 

metropolitan area, along with the government master file (GMF) data, were used to design the 

alternative LMR trunked radio systems. 

In comparing the results of the Washington, DC measurements to the results of the Denver 

measurements, similar data on usage were obtained for the 162–174 MHz band for all channels 

spaced 12.5 kHz apart. The difference in usage between the two sets of measurements was only 

0.3 percent. The percentage distributions for when the usage peaked are also very similar to each 

other. These consistent results imply that the technology and data process techniques used for the 

Washington, DC and Denver measurements can be used for future LMR measurements at other 

locations. For the 406–420 MHz band, the difference in usage between the two measurements 

was 1.65 percent. It is unknown why this occurred and the reasons for it may be investigated. It 

is possible that this difference is merely due to the fact that there are more Federal users in the 

Washington, DC area than in the Denver metropolitan area. 

The intent of these measurements was not to examine details of performance and use for the 

characterization of individual channels, but rather, for the channels in aggregate. Individual 

channel information, as well as more extensive measurements, would be required for a detailed 

engineering design for a next generation system. 

MEASUREMENTS TO CHARACTERIZE LAND MOBILE CHANNEL OCCUPANCY 

FOR FEDERAL BANDS 162–174 MHZ AND 406–420 MHZ IN THE DENVER, CO 

AREA 

John E. Carroll, J. Randy Hoffman, and Robert J. Matheson1

 This report describes field measurements to characterize Land Mobile Radio 

(LMR) channel occupancy of Federal bands 162–174 megahertz (MHz) and 

406–420 MHz at a single location overlooking the Denver, Colorado metropolitan 

area. This is part of the National Telecommunications and Information 

Administration effort to improve the spectrum efficiency of Federal radio usage. 

Measurements of the received radio traffic levels in these LMR frequency bands 

were performed over an 8-day period for the purpose of determining radio 

channel usage within the receiver spatial coverage of approximately 

100-kilometer (km) radius for base stations, 50-km radius for mobile units, and 

25-km radius for handheld units. The measurements were made using newly 

developed techniques that digitize as much as a 5-MHz segment of spectrum and 

process it to obtain simultaneous signal levels of up to 400 individual LMR 

channels. These techniques provided faster measurements, but also allowed 

enhanced post-processing of the data to remove effects of impulsive noise-like 

sources. 

Key words: channel occupancy; channel usage; Federal radio usage; Land Mobile Radio (LMR); 

measurements; spectrum efficiency 

1 INTRODUCTION 

In May 2003, President Bush established the Spectrum Policy Initiative to promote the 

development and implementation of a United States spectrum policy for the 21st century. In 

response to the Spectrum Policy Initiative, the Secretary of Commerce established a Federal 

Government Spectrum Task Force and initiated a series of public meetings to address policies 

affecting spectrum use by the Federal, state, and local governments, and the private sector. The 

recommendations resulting from these activities were included in two reports released by the 

Secretary of Commerce in June 2004. Based on the recommendations contained in these reports, 

the President directed the Federal Agencies on November 30, 2004 to plan the implementation of 

the 24 recommendations contained in the reports. One of the recommendations directed the 

National Telecommunications and Information Administration (NTIA) to develop analytic 

approaches, software tools, and engineering techniques for evaluating and improving the 

efficiency and effectiveness of Federal spectrum use. 

As discussed in the Spectrum Policy Initiative reports, the radio frequency (RF) spectrum is a 

critical resource that is used by the Federal Government to perform congressionally mandated 

 

1

 The first two authors are with the Institute for Telecommunication Sciences, National Telecommunications and 

Information Administration, U.S. Department of Commerce, Boulder, CO 80305. Mr. Matheson was formerly with 

the Institute. 
missions. Efficient use of the spectrum is one of the cornerstones for obtaining maximum usage 

of the available spectrum. NTIA and other Federal Agencies realize that the primary way to 

satisfy the growing demand for spectrum in the Land Mobile Radio (LMR) frequency bands is to 

employ more spectrum efficient technologies. 

As part of the effort to meet these objectives, ITS undertook a series of channel occupancy and 

usage measurements at a single location in the Denver metropolitan area in the 162–174 and 

406–420 MHz LMR bands, the results of which are described in this report. The results of these 

channel occupancy measurements can further be used to specify the overall performance 

objectives of LMR systems employing different technologies (e.g., trunking). 

1.1 Objective 

There were two objectives for this project. The first objective was to monitor each assignable 

12.5-kilohertz (kHz) and 25-kHz channel in the 162–174 MHz and 406–420 MHz bands in the 

Denver metropolitan area to determine the amount of time those channels contained power above 

specific thresholds, and to present statistical analysis of channel occupancy based on the number 

of occurrences exceeding the threshold. The second objective was to evaluate the measurement 

techniques and technology that were used to obtain the channel occupancy and usage data for the 

LMR bands. 

1.2 Approach 

Using the Radio Spectrum Measurement Science fourth generation measurement system (RSMS4), the measurements were performed during the course of 8 consecutive days (October 26 to 

November 3, 2005). The measurement system was designed for a receiver spatial coverage of 

approximately 100-kilometer (km) radius for base stations and repeaters, 50-km radius for 

mobile units, and 25-km radius for portable units.2

 Data were acquired continuously, 24 hours 

per day, over the course of the 8-day period and then analyzed for Federal bands 162–174 MHz 

and 406–420 MHz to furnish channel loading statistics. 

The measurements were made using newly developed techniques that digitize up to a 5-MHz 

segment of spectrum and process it to obtain simultaneous signal levels of up to 400 individual 

LMR channels. These techniques provided faster measurements and also allowed enhanced postprocessing of the data to remove the effects of impulsive noise-like sources. 

In this report, channels are considered to be occupied (i.e., in use) whenever the channel contains 

RF power above a certain received threshold level. The measurements were made and recorded 

so that variable threshold levels could be used for purposes of analyzing the effects of external 

noise-like sources and other factors. This definition of occupancy is generally consistent with 

other definitions of usage, although the choice of received power detection threshold levels is not 

necessarily uniform among researchers. By some definitions a channel may be considered “in 

use” even if no traffic is being carried during the time of measurement. For instance, a channel 

 

2

 Typical reuse distances for base stations and repeaters are approximately 100km. 

2
3

being used by a Secret Service agent protecting the President may not carry traffic (not occupied) 

unless there is an emergency. However, the channel is “in use” in the sense that personnel are 

monitoring the channel and ready to utilize it should a situation require it. In this report, “usage” 

is used interchangeably with the term “occupancy,” which means carrying traffic — not simply 

being monitored.
2 FIELD MEASUREMENTS DESCRIPTION 

The measurements characterizing the Denver metropolitan area LMR occupancy were performed 

using the same methodology, hardware, configurations, and post-measurement techniques as the 

measurements to characterize the Washington DC area [2]. 

2.1 Site Selection 

These LMR channel occupancy measurements were made using NTIA’s RSMS-4 mobile 

laboratory at a site on the grounds of the Exempla Colorado Lutheran Home facility in Arvada, 

located at coordinates N39° 49' 39.28", W105° 4' 50.21" (Figure 1). The measurements were 

conducted 24 hours per day over the course of 8 consecutive days (Wednesday, October 26th to 

Thursday, November 3rd, 2005). The site was chosen for several reasons. It is elevated above 

the surrounding Denver metropolitan area and there is little LMR activity by mobile users in 

close proximity to the measurement site. In addition, there are relatively few strong base stations 

nearby that could overdrive or mask weaker signals from the measurement system. 

Figure 1. RSMS mobile lab at measurement location. 

4
Figure 2 shows an aerial view of the Denver metropolitan area with a marker designating the 

location of the measurement system. Figures 3 and 4 show predicted coverage plots using the 

Longley-Rice irregular terrain model (maximum receiver sensitivity)3

 for three different 

transmitter scenarios: 1) a 100-watt (W) transmitter with gain of 3 decibels relative to isotropic 

(dBi) and a 30-meter (m) antenna height (typical base station), 2) a 50-W transmitter with 0-dBi 

gain and a 1.5-m antenna height (typical mobile unit), and 3) a 10-W transmitter with -3-dBi gain 

and a 1.0-m antenna height (portable unit).4 Figures 3 and 4 are for the 162–174 MHz and 

406–420 MHz frequency bands respectively. 

Figure 2. Aerial view of the Denver metropolitan area and the location of the measurement 

system. 

 

3

 The noise figures of the 162–174 MHz and the 406–420 MHz system are 13.9 dB and 9.9 dB respectively. 4

 More realistically, portable units have a maximum output of 5–6 W, and therefore, the coverage plots for portable 

units may be slightly less than that shown in Figures 3 and 4. 

5
6

Figure 3. Coverage plot for the 162–174 MHz band using the minimum receiver threshold. 

Figure 4. Coverage plot for the 406–420 MHz band using the minimum receiver threshold. 
3 ANALYSIS AND RESULTS 

Graphs and tables summarizing the usage for the different bands are included in this section, as 

well as in Appendix A. Since the same methodology, hardware, configurations, and postmeasurement techniques were used as in the Washington DC area measurements, the detailed 

discussion of the various methods of statistical analysis is given in Section 5 of [2]. 

3.1 Time Scenarios 

Both frequency groupings were analyzed according to five different time scenarios, as follows: 

1. Entire week: Data analyzed as a whole for the entire week beginning Wednesday, 

October 26, 2005 at 2 p.m. through Thursday, November 3, 2005 at 10 a.m., 

independent of time or date. 

2. Date and time of day: Data analyzed according to the date and time, in one-hour 

blocks. 

3. Time of day for any day: Data analyzed according to time, in one-hour blocks, 

between 12 a.m. and 12 a.m. (24 hours later), independent of date or day. 

4. Time of day for weekdays: Data analyzed according to time, in one-hour blocks, 

between 12 a.m. and 12 a.m. (24 hours later) only for weekdays, independent of the 

day. 

5. Time of day for weekends: Data analyzed according to time, in one-hour blocks, 

between 12 a.m. and 12 a.m. (24 hours later) only for weekend days, independent of 

the day. 

3.2 High Occupancy Channels 

There were no high occupancy channels (HOCs)5

 detected in the 162–174 MHz band and 12 

HOCs (representing 1.1 percent of channels) in the 406–420 MHz band. 

Table 1. Total Number of Statistically Analyzed Channels Spaced 12.5 kHz Apart 

Frequency band Number of channels analyzed 

162–174 MHz 943 

406–420 MHz (including HOCs) 1112 

406–420 MHz (excluding HOCs) 1100 

 

5

 Section 5.4 of [2] provides a detailed description of HOCs. 

7
8

3.3 Measurement Results 

Figures 5 through 27 summarize the measurement results. For an explanation of how to interpret 

Figures 5 through 27, see [2]. As a quick reference, Tables 2 and 3 provide figure numbers for 

the various plot types. For statistics that do not provide results for multiple threshold levels, only 

the minimum threshold is used, the values of which are listed in Table 4. 

 

Table 2. Figure Numbers for Graphs in the 162–174 MHz Band 

Figure Number 5 6 7 8 9 10 11 12 13 14 15 A-1

Hourly Band Usage x x 

Busiest Hour of the Week for Each Channel x

Band Occupancy by Time-of-Day x x x

% Hourly Channel Percent Occupancy 

Values Exceeding % Usage x 

% Channels Exceeding % Usage for 

Channel Percent Occupancy x 

% Channels Exceeding % Usage for Busiest 

Usage by Time-of-Day for Each Channel x 

APD of Channel Power Values x x 

% Channels Exceeding a Given % of Hours 

at Greater than or Equal to a Given % Usage x 

Multiple Thresholds x x 

Multiple Channelization Scenarios x x x x x x 

Multiple Time Scenarios x

Entire Week x x x x x x 

Date and Time of Day x x x 

Time for Any Day x x x

Weekdays x

Weekend Days x

All Channels x x x x x x x x x x x x 

25-kHz Channelization x x x x x x 

12.5-kHz Channelization x x x x x x 
Table 3. Figure Numbers for Graphs in the 406–420 MHz Band 

Figure Number 16 17 18 19 20 21 22 23 24 25 26 27 A-2

Hourly Band Usage x x x 

Busiest Hour of the Week for Each 

Channel x 

Band Occupancy by Time-of-Day x x x 

% Hourly Channel Percent 

Occupancy Values Exceeding % 

Usage 

x 

% Channels Exceeding % Usage for 

Channel Percent Occupancy x 

% Channels Exceeding % Usage for 

Busiest Usage by Time-of-Day for 

Each Channel 

x 

APD of Channel Power Values x x 

% Channels Exceeding a Given % 

of Hours at Greater than or Equal to 

a Given % Usage 

x 

Multiple Thresholds x x 

Multiple Channelization Scenarios x x x x x x x 

Multiple HOC Scenarios x x 

Multiple Time Scenarios x 

Including HOC x x x x 

Excluding HOC x x x x x x x x x x x 

Entire Week x x x x x x 

Date and Time of Day x x x x 

Time for Any Day x x x 

Weekdays x 

Weekend Days x 

All Channels x x x x x x x x x x x x x 

25-kHz Channelization x x x x x x x 

12.5-kHz Channelization x x x x x x x 

9
Table 4. Minimum Threshold Values 

Frequency band dBm at measurement 

antenna terminals 

dBμV/m field strength 

(0 dBi gain antenna) 

162–174 MHz Band -113 8 

406–420 MHz Band -119 6 10 

Several of the channel-usage graphs show anomalies that require further explanation (the term 

anomaly refers to data that do not reflect what is truly occurring). As Figures 5 and A-1 show, 

there are three different times (on Monday afternoon, Tuesday morning, and Thursday morning) 

in which all data plots exceed 2.0 percent usage. Examining this data in greater detail revealed 

the presence of broadband, noise-like sources that were high enough to raise the statistics for 

mean usage on the minimum threshold plot but were not high enough to be detected and 

removed by the processing techniques described in section 4.1 of [2]. This conclusion was drawn 

by examining the data contained in Figures 6 and 9. Figure 6 shows large numbers of adjacent 

channels exhibiting their busiest hour to coincide with the presence of increased noise-like 

sources. As there are currently no licensed wide-band frequency allocations in either band, these 

usage anomalies cannot be attributed to them. This conclusion is reinforced by Figure 9 where a 

spike in usage occurs at the 2 p.m. hour from a noise-like source that exceeds the minimum 

threshold (-113 dBm), but not the next highest threshold (-110 dBm). As this data represents the 

mean usage across the entire measurement band, a large number of frequencies must have 

experienced the presence of a noise-like source at that hour. 

In Figure 8, which shows the Band Occupancy by Time-of-Day plot, the same usage spike as 

noted above is visible. This usage spike would appear to be the time for the Maximum Band 

Usage value. However, this data is contaminated by the presence of a broadband, noise-like 

source, and although it is possible that the maximum usage does occur at 2 p.m., the results are 

inconclusive for that time period. For this reason, the maximum value at 2 p.m. is discarded in 

favor of the next-highest value occurring at 11 a.m. For amplitude probability distribution (APD) 

plots, time periods during which this noise-like source was present were excluded from analysis. 

To improve readability of the Hourly Band Usage plots, the noise-like source anomalies are 

often cut off by the top of the graphs, since this data is not relevant to analysis. As shown in 

Figure A-2, none of the anomalies that were manifested in the 162–174 MHz band occurred in 

the 406–420 MHz band. 

 

To give some indication of the degree to which assignments have migrated to the 12.5-kHz 

channel spacing, several of the graphs show statistical summaries for three different 

channelization schemes. 

As described in Section 2.1 of [2], these schemes are referred to as: All channels spaced 12.5 kHz 

apart, Old 25 kHz channelization, and New 12.5 kHz channelization.

 

6

 For the Washington, DC measurements, the minimum threshold was -117 dBm. For the Denver measurements, the 

measurement system had been improved to give an additional 2 dB of dynamic range. 

10
3.3.1 Results for 162–174 MHz Band 

Figure 5. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 162–174 MHz band (minimum threshold).7

 

7

 The large usage anomalies, exceeding 2.0 percent usage, occurring on Monday, Tuesday, and Thursday are due to 

external, noise-like sources received by the measurement system. Examining this data in greater detail revealed the 

presence of noise-like sources that were high enough to raise the statistics for mean usage on the minimum threshold 

plot but were not high enough to be detected and removed by the processing techniques described in Section 4.1 of 

[2]. 

11
Figure 6. Busiest Hour of the Week for Each Channel in the 162–174 MHz band. 

12
13

Figure 7. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during different 

24-hour time scenarios in the 162–174 MHz band (minimum threshold, all channels spaced 12.5 

kHz apart).8

 

8

 In Figures 7, 8, and 9, there was a presence of a noise-like source around 2 p.m. (1400 hours) that evaded postprocessing techniques. It is possible that the maximum usage does occur at 2 p.m., but, because the data is 

contaminated, no definitive conclusion can be reached about that specific measurement point for the minimum 

threshold. 
Figure 8. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during the 

course of 24 hours, independent of the date, for different channelization scenarios in the 162–174 

MHz band (minimum threshold).9

 

9

 As discussed in [2], the processed data in Figures 8 and 9 contain measurements on both Specific Location 

Assignments (base station has a fixed latitude and longitude location) and Area Assignments (base station is not 

constrained to a specific location) from the GMF database. The Maximum Band Occupancy in Figure 8, which 

includes both types of assignments, is about 1.3 percent at 11 a.m. The Maximum Band Occupancy associated with 

each type of assignment (“Specific Location” vs. “Area”) will be different, since Area Assignments may or may not 

have been active during the measurement period within the measurement coverage area. 

14
Figure 9. Band Occupancy by Time-of-Day (percent of time and total Erlangs) using different 

thresholds, independent of the date, for all 943 channels in the 162–174 MHz band. 

15
Figure 10. Percent of Hourly Channel Percent Occupancy values exceeding a given percent 

usage over the course of the measurements for the 162–174 MHz band (minimum threshold). 

16
Figure 11. Percent of channels exceeding a given percent usage for Channel Percent 

Occupancy over the course of the measurements for the 162–174 MHz band (minimum 

threshold). 

17
Figure 12. Percent of channels exceeding a given percent usage for the Busiest Usage by Timeof-Day for Each Channel during weekdays only in the 162–174 MHz band (minimum threshold). 

18
Figure 13. APDs of Channel Power Values for channels in the 162–174 MHz band — entire 

week, independent of date or time for different channelizations (minimum threshold). 

19
20

Figure 14. APDs of Channel Power Values for all channels spaced 12.5 kHz apart in the 162–

174 MHz band for the busiest hour during the entire week independently for each frequency 

(minimum threshold). 
Figure 15. Cumulative distribution of the percent of channels that exceed a given percent of 

hours at greater than or equal to a given Hourly Channel Percent Occupancy (designated by 

legend) for all channels in the 162–174 MHz band (minimum threshold, entire week).10

 

10 Discrete steps in the “percent of hourly periods” occur because there are a discrete number of one-hour time slots 

over the course of the measurement. Since there were approximately 188 hours of measurement during the course of 

the 8 days, a single one-hour time slot represents a “percent of hourly periods” of 0.53 percent, two hours represents 

approximately 1 percent, and three hours represents approximately 1.5 percent (consistent with the discrete steps 

seen in the figure above). 

21
3.3.2 Results for 406–420 MHz Band 

Figure 16. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 406–420 MHz band (excluding HOCs; minimum threshold). 

22
Figure 17. Busiest Hour of the Week for Each Channel in the 406–420 MHz band. 

23
Figure 18. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for the 406–420 MHz band (including HOCs; minimum threshold). 

24
Figure 19. Band Occupancy by Time-of-Day during different 24-hour time scenarios in the 

406–420 MHz band (excluding HOCs; minimum threshold). 

25
Figure 20. Band Occupancy by Time-of-Day (percent of time and total Erlangs) during the 

course of 24 hours, independent of the date, for different channelization scenarios in the 406–

420 MHz band (excluding HOCs; minimum threshold). 

26
Figure 21. Band Occupancy by Time-of-Day (percent of time and total Erlangs) using different 

thresholds, independent of the date, for all 1,100 channels in the 406–420 MHz band (excluding 

HOCs). 

27
Figure 22. Percent of Hourly Channel Percent Occupancy values exceeding a given percent 

usage over the course of the measurements for the 406–420 MHz band (minimum threshold). 

28
Figure 23. Percent of channels exceeding a given percent usage for Channel Percent 

Occupancy over the course of the measurements for the 406–420 MHz band (minimum 

threshold). 

29
Figure 24. Percent of channels exceeding a given percent usage for the Busiest Usage by Timeof-Day for Each Channel during weekdays only in the 406–420 MHz band (minimum threshold). 

30
Figure 25. APDs of Channel Power Values for channels in the 406–420 MHz band — entire 

week, independent of date or time for different channelizations (excluding HOCs; minimum 

threshold). 

31
32

Figure 26. APDs of Channel Power Values for all channels spaced 12.5 kHz apart in the 406–

420 MHz band for the busiest hour during the entire week, independently for each frequency for 

different HOC scenarios (minimum threshold).
Figure 27. Cumulative distribution of the percent of channels that exceed a given percent of 

hours at greater than or equal to a given Hourly Channel Percent Occupancy (designated by 

legend) for all channels in the 406–420 MHz band (excluding HOCs; minimum threshold).

33
4 SUMMARY 

The measured data presented in this report characterize channel usage of LMR systems operating 

in the 162–174 and 406–420 MHz frequency bands in the Denver metropolitan area. The 

analysis of the data is used to present the percent usage for a typical or representative channel 

during an 8-day measurement period (October 26 to November 3, 2005) using sampling 

procedures for the measurements. 

A summary of the measurement results for channel usage and diurnal patterns for each band is 

given in Sections 4.1 through 4.2. There are several limitations to the measurements, however, 

that need to be considered. 

 

Because the measurement system coverage area for mobile and portable stations is not as 

extensive as for base stations and repeaters, and because terrain and structural obstruction may 

prevent adequate reception of these mobile radio signals by the measurement system, the usage 

statistics may not fully reflect the actual usage within the bands. However, for each transmission 

by a portable or mobile station there is usually a corresponding transmission response from a 

base station or repeater that reflects that usage. Therefore, for the worst case, where no portable 

and mobile station transmissions are detected, the measured base station usage would need to be 

doubled (assuming no talk-around). In reality, the usage statistics lie somewhere in between 

these two extremes, since some signals from mobile and portable stations were detected by the 

measurement system. It is also possible that the measurement system coverage area for base 

stations is extensive enough to detect frequency reuse, thus reflecting a higher than expected 

average usage. 

There are some assignments that, while included in the overall statistical analysis, are not used 

for LMR transmissions, such as hydrology channels. Other assignments cannot be detected for 

reasons described in the previous paragraph. The received power from some assignments may be 

below the measurement system’s sensitivity and, therefore, not detected. Some channels may be 

assigned for “listening only” in the sense that they infrequently carry traffic but are monitored 

continually for emergency transmissions. In every case, the result is that the usage statistics may 

show less usage than would be expected if the analysis were performed only on channels that are 

reserved for transmission and can be detected within the measurement receiver coverage. 

Furthermore, any 12.5-kHz channel that has a wideband assignment adjacent to it generally 

cannot be used within the measurement system coverage area and therefore, would not show any 

activity. 

Out of the 36 hydrology channels (see Definitions) in the 162–174 MHz band and the 12 

hydrology channels in the 406–420 MHz band, none exceeded 80 percent usage (some displayed 

very little, if any, usage), so all were included in the overall LMR occupancy statistics. Upon 

closer examination, it was determined that the hydrology channels in the 162–174 MHz band had 

a mean usage of 1.2 percent and the hydrology channels in the 406–420 MHz band had a mean 

usage of 0.0 percent. For the 162–174 MHz band, the inclusion of hydrology channels increased 

the mean usage by 0.03 percent, and for the 406–420 MHz band, the inclusion of hydrology 

channels decreased the mean usage by 0.01 percent. 

34
While every effort was made to minimize the effects of interference from noise-like sources, as 

described in Section 4.1 of [2], there were occasional periods when broadband, noise-like 

sources raised the power in the entire band enough for individual channels to exceed the 

detection threshold, but not enough to be identified as corrupted data and discarded from the 

analysis. It is difficult to determine precisely how often this occurred, but it may have occurred 

enough to skew the mean usage values somewhat towards higher than expected usage values. 

Much of the data in this report is presented in the form of “mean usage” which is meant to 

convey “typical” usage by a channel. However, because the percent usage statistics are not 

Gaussian distributed, and because, as shown in Figure 12, there are a few channels with 

relatively high usage (20 percent of the channels with greater than 2.3 percent usage), but far 

more channels with relatively low usage (30 percent between 0.5 to 1.6 percent and 40 percent 

less than 0.5 percent), the mean is skewed, due to outliers, towards a larger value than what one 

might think of as “typical.” In this case, the median may be more representative of a “typical” 

channel usage and can be extracted from the cumulative distribution plots in Figures 10, 11, and 

12 (detailed analysis of the plots is described in Section 5.6 of [2]). 

Because most of the channels in these bands are statically assigned to networks or individual 

users, as opposed to dynamically assigned as is the case with trunked systems (see Definitions), 

many of these channels are reserved for high priority usage in which communication must be 

available at all times for a limited number of users. It also should be noted that agencies may 

have channel usage that deviates from these values. Likewise, none of these measurements were 

made during a major emergency that might have greatly increased a channel’s use. 

The channel occupancy measurements in this report can be used for specifying the overall 

performance objectives of a hypothetical communications system using a different technology 

(e.g., trunking). By designing the hypothetical system to provide the same overall 

communications capability as the existing LMR systems, the existing and hypothetical systems 

could then be compared to examine relative total spectrum usage (number of channels required 

for each system). For example, [4] used channel occupancy measurements from the Washington 

DC metropolitan area [2], along with the GMF data from [5], to design and assess several 

hypothetical trunked LMR systems, and compared their spectrum usage to conventional systems 

in the same area. 11

The intent of the measurements was not to examine details of performance and use for the 

characterization of individual channels, but rather, for the channels in aggregate. This individual 

channel information, as well as more extensive measurements, may be required for a detailed 

engineering design for a next generation system. 

4.1 Overall Results 

Hourly Band Usage within the measurement system coverage area varies between 0.3–1.6 

percent (Figures 5 and 16) for the two measured bands, but shows the busiest hours are between 

 

11 Reference [4] assesses several hypothetical LMR system designs and develops a comparison of the spectrum 

resources used by alternative trunked LMR system designs and conventional LMR systems. Reference [5] analyzes 

Federal frequency assignment data to assess the geographic coverage of existing conventional LMR systems. 

35
7 a.m. and 5 p.m., with the minimum usage near midnight. Results also show that the newly 

created 12.5-kHz channels are not yet used as much as the old 25-kHz channels. Note that these 

are average statistics, and usage for individual channels by agencies may deviate significantly 

from the overall band usage. 

4.1.1 Results for 162–174 MHz band 

For a mean12 detection threshold of -113 dBm in the 162–174 MHz band, Band Occupancy by 

Time-of-Day within the measurement system coverage area is between 0.6–1.5 percent for all 

channels spaced 12.5 kHz apart, 0.8–1.6 percent for the old 25-kHz channels, and 0.4–1.2 

percent for the new 12.5-kHz channels (Figure 8). The highest conclusive value of the Band 

Occupancy by Time-of-Day represents the Maximum Band Occupancy, which is 1.3 percent for 

all channels spaced 12.5 kHz apart and includes both Specific Location and Area frequency 

assignments. Note that the Maximum Band Occupancy does not occur at the 2 p.m. hour, which 

is shown in Figure 8 to have the highest usage (1.5 percent) since the data at that hour was 

contaminated by an external noise-like source and is suspect. Instead, the 1.3 percent value 

occurring at the 11 a.m. hour was selected. When the Maximum Band Occupancy for channels 

spaced 12.5 kHz apart is calculated based on only the Specific Location Assignments, the value 

is 1.9 percent.13

The Band Occupancy by Time-of-Day for conventional LMR systems can be compared to 

allowable call-blockage (typically referred to as Grade of Service) as recommended in the Final 

Report of the PSWAC [3]. In that report the committee recommends that blockage not exceed 

“one call for service per one hundred attempts during the average busy hour.” That translates to 

no more than 1 percent usage for multi-user conventional systems where channels are assigned 

statically. Since the systems measured in the 162–174 MHz band are conventional systems, the 

measured usage during the busiest hour of 1.3 percent is relatively consistent with the 

recommendations by the PSWAC. 

 

For a mean detection threshold of -113 dBm, the overall Percent Band Usage for the 

162–174 MHz band during weekdays is 0.99 percent over a 24-hour period, 1.12 percent 

between 8 a.m. and 5 p.m., and 2.25 percent for the Average of Busiest Usage by Hour (Table 

A-2). For Busiest Usage by Time-of-Day, 40 percent of the channels exceed a usage of 1 percent, 

while 10 percent of the channels exceed 5 percent, and 1 percent of the channels exceed 30 

percent (Figure 12). 

 

12 Because the detection threshold, especially for the minimum threshold, is not constant across the frequency 

channels, threshold values given for statistical analysis are stated in terms of “mean” threshold power. 

13 The Specific Location Assignments, as researched by OSM, refer to the frequency assignments in the GMF for 

LMR base stations that have a fixed latitude and longitude location. The other frequency assignments in the GMF 

are the Area Assignments that have base stations not constrained to a specific location. 

36
37

4.1.2 Results for 406–420 MHz band 

For a mean detection threshold of -119 dBm in the 406–420 MHz band (HOCs excluded), Band 

Occupancy by Time-of-Day within the measurement system coverage area varies between 

0.65–0.95 percent for all channels spaced 12.5 kHz apart, 0.95–1.45 percent for the old 25-kHz 

channels, and 0.30–0.45 percent for the new 12.5-kHz channels (Figure 20). The highest 

conclusive value of the Band Occupancy by Time-of-Day represents the Maximum Band 

Occupancy, which is 0.95 percent for all channels spaced 12.5 kHz apart. 

For a mean threshold level of -119 dBm, overall Percent Band Usage for the 406–420 MHz band 

during weekdays is 0.82 percent over a 24-hour period, 0.94 percent between 8 a.m. and 5 p.m., 

and 1.53 percent for the Average of Busiest Usage by Hour (Table A-5). For Busiest Usage by 

Time-of-Day, 12 percent of the channels exceed 1 percent, while 10 percent of the channels 

exceed 2 percent, and 1 percent of the channels exceed 40 percent (Figure 24). 

4.2 Diurnal Patterns for Both Bands 

In the 162–174 MHz band, the diurnal behavior was similar, irrespective of whether they were 

measured for all days, weekdays or weekends. The highest overall usage occurred on weekdays 

(Figure 7), with the normal daylight hours showing the most activity. Curiously, there was a 

duration of time in the mid-morning hours where the weekend use dominated the weekday use. 

In the 406–420 MHz band, a distinct difference in diurnal pattern can be noted between the 

weekday and weekend cases (Figure 19), with the usage being higher during normal daylight 

hours on the weekdays and outside of normal daylight hours on weekends. Usage on the 

weekends is decreased by a factor of as much as 2 during normal daylight hours when compared 

to weekdays. There was a small duration of time in the early morning hours where usage was 

higher for the weekend case when compared to the weekday case. 

When examining the Busiest Hour of the Week for Each Channel, the busiest hours are more 

broadly grouped in the daytime hours (Figures 6 and 17). There are a few occurrences where 

blocks of adjacent frequencies appear to have the busiest hour all at the same time. However, 

such occurrences are not typical. Based on our data, we conjecture that whenever large numbers 

of adjacent frequencies appear to become busy at the same time, there is a possibility that the 

measurements were affected by broadband noise-like RF energy. 

4.3 Evaluation of Measurement Techniques and Technologies 

ITS developed custom hardware and software to make LMR channel occupancy measurements 

for the bands 162–174 and 406–420 MHz in the Washington, DC and Denver metropolitan areas. 

The measurement techniques and equipment described in [2] can be used to perform future LMR 

measurements at other locations. To improve the techniques, future LMR measurements will 

have more sampling time per channel and remove hydrology channels from the post processing. 

At the same time, future post processing techniques should provide the ability to gain access to 

mid-level calculations or steps and permit the viewing of intermediate results. 
5 ACKNOWLEDGEMENTS 

This project involved technical contributions by various individuals at the Institute for 

Telecommunication Sciences. The authors recognize Dr. William Kissick for his vision and 

leadership, Brent Bedford for his technical and theoretical support, Iris Tobias for her support, 

Yeh Lo for his work on the preselectors as well as other system development, Rick Statz and 

Steve Engelking for software development, and Margaret Luebs for editorial review. 

The authors also wish to recognize Ed Drocella, Robert Sole, Bernard Joiner, Gary Patrick, Kim 

Cai, Yang Wang, and Dave Anderson from OSM for their support. 

6 REFERENCES 

[1] W.A. Kissick, Ed., “The temporal and spectral characteristics of ultrawideband signals,” 

Appendix A, NTIA Report 01-383, Jan. 2001, Available: 

<http://www.its.bldrdoc.gov/pub/ntia-rpt/01-383/>. 

[2] J.R. Hoffman, R.J. Matheson, and R.A. Dalke, “Measurements to characterize land mobile 

channel occupancy for Federal bands 162–174 MHz and 406–420 MHz in the Washington, 

D.C., area,” NTIA Report 07-448, Jul. 2007, Available: 

<http://www.its.bldrdoc.gov/pub/ntia-rpt/07-448/>. 

[3] Public Safety Wireless Advisory Committee (PSWAC) Report, Spectrum Requirements 

Subcommittee (SRSC) Final Report, Volume 2, Appendix D, Page 76, Sept. 1996. 

[4] K. Cai, B. Joiner, R.J. Matheson, E. Drocella, G. Patrick, D. Anderson, “Assessment Of 

alternative future Federal land mobile radio systems,” NTIA Report 08-451, Dec. 2007, 

Available: <http://www.ntia.doc.gov/osmhome/reports.html>. 

[5] G. Patrick, C. Hoffman, R.J. Matheson, F. Najmy, R. Wilson, “Federal land mobile radio 

operations in the 162–174 MHz Band in the Washington, D.C. area, Phase 1: Study of 

agency operations,” NTIA Report 06-440, Aug. 2006, Available: 

<http://www.ntia.doc.gov/osmhome/reports.html>.

38
APPENDIX A: SUPPLEMENTAL MEASUREMENT RESULTS 

This appendix provides additional results of usage at each hour for different thresholds and tables 

summarizing average usage. For an explanation of how to interpret these additional results, see 

Section 5.6 of [2], specifically pages 34, 35, and 44. The first section shows, for the purpose of 

discussing anomalies, usage data for each one-hour block during the course of the measurements. 

The remaining two sections provide mean usage within the receiver’s spatial coverage for the 

two frequency bands. 

A.1 Usage for Each One-hour Block During the Course of the Measurements 

Figure A-1. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for all 943 channels in the 162–174 MHz band. 

39
Figure A-2. Hourly Band Usage (percent of time and total Erlangs) during the course of the 

measurements for all 1,100 channels in the 406–420 MHz band (excluding HOCs). 

40
41

A.2 Percent Band Usage for the 162–174 MHz Band 

Tables A-1 through A-3 contain the Percent Band Usage data for the 162–174 MHz band for the 

entire week, weekdays only, and weekends only. For an explanation of how to interpret these 

tables, see Section 5.6 of [2]. The data is presented in terms of a 24-hour period and a period of 8 

a.m. to 5 p.m. for each table. Note that for the entire week and weekdays only tables, data is 

included for the Average of Busiest Usage by Hour. That information is not relevant to the 

weekend only table and is not included for those measurement times since the busiest times 

happen during the weekdays. 

Table A-1. Percent Band Usage and Average of Busiest Usage by Hour During the Entire Week

for All 943 Channels in the 162–174 MHz Band 

All Days Mean Detection Threshold 

Threshold (dBm) -113 -110 -100 -90 -80 

Threshold (dBμV/m) 8 11 21 31 41 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.94 ± 0.0114 0.53 0.15 0.04 0.03 

Average of Busiest Usage by Hour 2.04 ± 0.07 14 Not Applicable 

% Band Usage (8 a.m. – 5 p.m.) 1.07 ± 0.02 14 0.57 0.16 0.06 0.04 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -113 dBm is 8.86 ((0.94 / 100) * 943). 

 

14 99 percent confidence level – assuming an average message length of no longer than 5 seconds. 
Table A-2. Percent Band Usage and Average of Busiest Usage by Hour During Weekdays Only

for All 943 Channels in the 162–174 MHz Band 

All Days Mean Detection Threshold 

Threshold (dBm) -113 -110 -100 -90 -80 

Threshold (dBμV/m) 8 11 21 31 41 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.99 ± 0.01 15 0.53 0.16 0.05 0.03 

Average of Busiest Usage by Hour 2.25 ± 0.08 15 Not Applicable 

% Band Usage (8 a.m. – 5 p.m.) 1.12 ± 0.02 15 0.54 0.17 0.07 0.05 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -113 dBm is 9.34 ((0.99 / 100) * 943).

Table A-3. Percent Band Usage and Average of Busiest Usage by Hour During Weekend Days 

Only for All 943 Channels in the 162–174 MHz Band 

All Days Mean Detection Threshold 

Threshold (dBm) -113 -110 -100 -90 -80 

Threshold (dBμV/m) 8 11 21 31 41 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.78 ± 0.0115 0.52 0.14 0.04 0.03 

% Band Usage (8 a.m. – 5 p.m.) 0.94 ± 0.01 15 0.63 0.13 0.04 0.03 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -113 dBm is 7.36 ((0.78 / 100) * 943).

 

15 99 percent confidence level – assuming an average message length of no longer than 5 seconds. 

42
43

A.3 Percent Band Usage for the 406–420 MHz Band 

Tables A-4 through A-6 contain the Percent Band Usage data for the 406–420 MHz band for the 

entire week, weekdays only, and weekends only. For an explanation of how to interpret these 

tables, see Section 5.6 of [2]. The data is presented in terms of a 24-hour period and a period of 8 

a.m. to 5 p.m. for each table. Note that for the entire week and weekdays only tables, data is 

included for the Average of Busiest Usage by Hour. That information is not relevant to the 

weekend only table and is not included for those measurement times since the busiest times 

happen during the weekdays. 

Table A-4. Percent Band Usage and Average of Busiest Usage by Hour During the Entire Week

for All 1,100 Channels in the 406–420 MHz Band (Excluding HOCs) 

All Days Mean Detection Threshold 

Threshold (dBm) -119 -115 -106 -96 -86 

Threshold (dBμV/m) 10 14 23 33 43 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.76 ± 0.0116 0.54 0.37 0.30 0.26 

Average of Busiest Usage by 

Hour 1.35 ± 0.03 16 Not Applicable 

% Band Usage (8 a.m. – 5 p.m.) 0.84 ± 0.01 16 0.63 0.44 0.34 0.30 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -119 dBm is 8.36 ((0.76 / 100) * 1100).

 

16 99 percent confidence level – assuming an average message length of no longer than 5 seconds. 
Table A-5. Percent Band Usage and Average of Busiest Usage by Hour During Weekdays for All 

1,100 Channels in the 406–420 MHz Band (Excluding HOCs) 

All Days Mean Detection Threshold 

Threshold (dBm) -119 -115 -106 -96 -86 

Threshold (dBμV/m) 10 14 23 33 43 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.82 ± 0.0117 0.58 0.40 0.31 0.28 

Average of Busiest Usage by 

Hour 1.53 ± 0.03 17 Not Applicable 

% Band Usage (8 a.m. – 5 p.m.) 0.94 ± 0.01 17 0.70 0.49 0.37 0.33 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -119 dBm is 9.02 ((0.82 / 100) * 1100).

Table A-6. Percent Band Usage and Average of Busiest Usage by Hour During Weekend Days

for All 1,100 Channels in the 406–420 MHz Band (Excluding HOCs). 

All Days Mean Detection Threshold 

Threshold (dBm) -119 -115 -106 -96 -86 

Threshold (dBμV/m) 10 14 23 33 43 

Timescale Percent Band Usage 

% Band Usage (24 hours) 0.63 ± 0.0117 0.44 0.32 0.25 0.22 

% Band Usage (8 a.m. – 5 p.m.) 0.58 ± 0.0117 0.44 0.32 0.25 0.23 

Note: Erlangs can be calculated by multiplying the Percent Band Usage for any threshold by the number of channels. 

For example, mean Erlangs for a threshold of -119 dBm is 6.93 ((0.63 / 100) * 1100).

 

17 99 percent confidence level – assuming an average message length of no longer than 5 seconds. 

44
APPENDIX B: WASHINGTON, DC AND DENVER, CO MEASUREMENT 

RESULTS COMPARISON TABLES 

Tables B-1 and B-2 provide a summary and comparison of usage for the Washington, DC and 

Denver metropolitan area measurements in the two bands. Results in the 162–174 MHz band 

(Table B-1) show that the measurement data in these two areas indicate that Denver exhibits less 

usage. For example, the Maximum Band Occupancy for the 162–174 MHz band for all channels 

spaced 12.5 kHz apart was 1.6 percent for the DC area and 1.3 percent for the Denver 

metropolitan area. The percentage distributions for Busiest Usage by Time-of-Day also show a 

similar difference. The results show that the 162–174 MHz LMR band is being used to the 

expected degree in both metropolitan areas, with Washington, DC being the largest Federal LMR 

user area, and the Denver metropolitan area representing a medium-sized, dense Federal user 

area. The technology and data processing techniques used for the Washington, DC and Denver 

metropolitan area measurements can be used to perform future LMR measurements at other 

locations. 

For the 406–420 MHz LMR band (Table B-2), the Maximum Band Occupancy was 2.7 percent 

for the Washington, DC metropolitan area, and about 0.95 percent for the Denver metropolitan 

area. Washington, DC shows a much higher usage in this band than the Denver metropolitan 

area. One observed reason is that Washington, DC is the headquarters for many Federal agencies 

and has much more activity than the Denver metropolitan area. Since the 162–174 MHz band 

was highly congested in the Washington, DC area, agencies tended to move to the 406–420 MHz 

band for their new LMR systems when the technology was available. Additional reasons for the 

difference may be researched in the future. 

45
46

Table B-1. Usage Summary for Washington, DC and Denver Metropolitan Area Measurements 

in the 162–174 MHz LMR Band 

Usage Items Channel 

Spacing Washington DC Area* Denver, CO Area** 

Total Number of Channels Analyzed 1 12.5 kHz 934 943 

Mean Detection Threshold -113 dBm -113 dBm 

Band Occupancy by 

Time-of-Day 

all 12.5 kHz 0.6–1.6 percent 0.6–1.5 percent 

old 25 kHz 0.9–2.2 percent 0.8–1.6 percent 

new 12.5 kHz 0.2–1.2 percent 0.4–1.2 percent 

(Figure 30) (Figure 8) 

Maximum Band Occupancy 12.5 kHz 

1.6 percent for all 

channels 

1.3 percent for all 

channels 

(Figure 30) (Figure 8) 

2.1 percent for 

SLA only 2

1.9 percent for 

SLA only 2

Percent Band Usage (weekdays) 

12.5 kHz 

1.11 percent 0.99 percent 

Percent Band Usage (8 a.m. – 5 p.m.) 1.53 percent 1.12 percent 

Average of Busiest Usage by Hour 3.14 percent 2.25 percent 

(Table A-2) (Table A-2) 

Busiest Usage by Time-of-Day 12.5 kHz 

60 percent channels 

exceed 1 percent usage 

40 percent channels 

exceed 1 percent usage 

10 percent channels 

exceed 7 percent usage 

10 percent channels 

exceed 5 percent usage 

1 percent channels exceed 

34 percent usage 

1 percent channels exceed 

30 percent usage 

(Figure 34) (Figure 12) 

1 NOAA Channels and HOCs (usage > 80 percent) are excluded. 

2

 SLA: Specific Location Assignments 

* Reference figures and tables in parentheses refer to [2]. 

** Reference figures and tables in parentheses refer to this report. 
Table B-2. Usage Summary for Washington, DC and Denver Metropolitan Area Measurements 

in the 406–420 MHz LMR Band 

Usage Items Channel 

Spacing Washington DC Area* Denver, CO Area** 

Total Number of Channels Analyzed 1 12.5 kHz 1113 1100 

Mean Detection Threshold -117 dBm -119 dBm 2

Band Occupancy by Time-of-Day 

all 12.5 kHz 1.3–2.7 percent 0.65–0.95 percent 

old 25 kHz 2.2–4.1 percent 0.95–1.45 percent 

new 12.5 kHz 0.4–1.5 percent 0.3–0.45 percent 

 (Figure 42) (Figure 20) 

Maximum Band Occupancy 12.5 kHz 

2.6 percent for all 

channels 

0.95 percent for all 

channels 

(Figure 30) (Figure 20) 

Percent Band Usage (weekdays) 

12.5 kHz 

2.08 percent 0.82 percent 

Percent Band Usage (8 a.m – 5 p.m.) 2.67 percent 0.94 percent 

Average of Busiest Usage by Hour 4.29 percent 1.53 percent 

(Table A-6) (Table A-5) 

Busiest Usage by Time-of-Day 12.5 kHz 

44 percent channels 

exceed 1 percent usage 

12 percent channels 

exceed 1 percent usage 

10 percent channels 

exceed 13 percent usage 

10 percent channels 

exceed 2 percent usage 

1 percent channels 

exceed 60 percent usage 

1 percent channels 

exceed 40 percent usage 

(Figure 46) (Figure 24) 

1

 HOCs (usage > 80 percent) are excluded. 

2

 For the Washington, DC measurements, the minimum threshold was -117 dBm. For the Denver measurements, 

the measurement system was improved to give an additional 2 dB of dynamic range. 

* Reference figures and tables in parentheses refer to [2]. 

** Reference figures and tables in parentheses refer to this report. 

47
FORM NTIA-29 U.S. DEPARTMENT OF COMMERCE 

(4-80) NAT’L. TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION 

BIBLIOGRAPHIC DATA SHEET 

1. PUBLICATION NO. 

TR-08-455 

2. Government Accession No. 3. Recipient’s Accession No. 

4. TITLE AND SUBTITLE 

Measurements to Characterize Land Mobile Channel Occupancy for Federal 

Bands 162–174 MHz and 406–420 MHz in the Denver, CO Area 

5. Publication Date 

September 2008 

6. Performing Organization 

Code 

7. AUTHOR(S) 

John E. Carroll, J. Randy Hoffman, Robert J. Matheson 

9. Project/Task/Work Unit No. 

3152012-300 

8. PERFORMING ORGANIZATION NAME AND ADDRESS 

Institute for Telecommunication Sciences 

National Telecommunications & Information Administration 

U.S. Department of Commerce 

325 Broadway 

Boulder, CO 80305 

10. Contract/Grant No. 

11. Sponsoring Organization Name and Address 

National Telecommunications & Information Administration 

Herbert C. Hoover Building 

14th & Constitution Ave., NW 

Washington, DC 20230 

12. Type of Report and Period 

Covered 

14. SUPPLEMENTARY NOTES 

15. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a 

significant bibliography or literature survey, mention it here.) 

This report describes field measurements to characterize Land Mobile Radio (LMR) channel occupancy of Federal 

bands 162–174 megahertz (MHz) and 406–420 MHz at a single location overlooking the Denver, CO metropolitan 

area. This is part of the National Telecommunications and Information Administration effort to improve the 

spectrum efficiency of Federal radio usage. Measurements of the received radio traffic levels in these LMR 

frequency bands were performed over an eight-day period for the purpose of determining radio channel usage within 

the receiver spatial coverage of approximately 100 kilometer (km) radius for base stations, 50 km radius for mobile 

units, and 25 km radius for handheld units. The measurements were made using newly developed techniques that 

digitize as much as a 5 MHz segment of spectrum and process it to obtain simultaneous signal levels of up to 400 

individual LMR channels. These techniques provided faster measurements, but also allowed enhanced postprocessing of the data to remove effects of impulsive noise-like sources. 

16. Key Words (Alphabetical order, separated by semicolons) 

channel occupancy; channel usage; Federal radio usage; Land Mobile Radio (LMR); measurements; spectrum 

efficiency 

17. AVAILABILITY STATEMENT 

 F UNLIMITED. 

18. Security Class. (This report) 

Unclassified 

20. Number of pages 

 47 

19. Security Class. (This page) 

Unclassified 

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